Fuel cell technology is a relatively recent development in the automotive industry. It has been found that fuel cell power plants are capable of achieving efficiencies as high as 55%. Furthermore, fuel cell power plants emit only heat and water as by-products.
Fuel cells include three components: a cathode, an anode and an electrolyte which is sandwiched between the cathode and the anode and passes only protons. Each electrode is coated on one side by a catalyst. In operation, the catalyst on the anode splits hydrogen into electrons and protons. The electrons are distributed as electric current from the anode, through a drive motor and then to the cathode, whereas the protons migrate from the anode, through the electrolyte to the cathode. The catalyst on the cathode combines the protons with electrons returning from the drive motor and oxygen from the air to form water. Individual fuel cells can be stacked together in series to generate increasingly larger quantities of electricity.
In a Polymer-Electrolyte-Membrane (PEM) fuel cell, a polymer electrode membrane serves as the electrolyte between a cathode and an anode. The polymer electrode membrane currently being used in fuel cell applications requires a certain level of humidity to facilitate conductivity of the membrane. Therefore, maintaining the proper level of humidity in the membrane, through humidity/water management, is very important for the proper functioning of the fuel cell. Irreversible damage to the fuel cell will occur if the membrane dries out.
In order to prevent leakage of the hydrogen fuel gas and oxygen gas supplied to the electrodes and prevent mixing of the gases, a gas-sealing material and gaskets are arranged on the periphery of the electrodes, with the polymer electrolyte membrane sandwiched there between. The sealing material and gaskets are assembled into a single part together with the electrodes and polymer electrolyte membrane to form a membrane and electrode assembly (MEA). Disposed outside of the MEA are conductive separator plates for mechanically securing the MEA and electrically connecting adjacent MEAs in series. A portion of the separator plate, which is disposed in contact with the MEA, is provided with a gas passage for supplying hydrogen fuel gas to the electrode surface and removing generated water vapor.
Because the proton conductivity of PEM fuel cell membranes deteriorates rapidly as the membranes dry out, external humidification is required to maintain hydration of the membranes and sustain proper fuel cell functioning. Moreover, the presence of liquid water in automotive fuel cells is unavoidable because appreciable quantities of water are generated as a by-product of the electrochemical reactions during fuel cell operation. Furthermore, saturation of the fuel cell membranes with water can result from rapid changes in temperature, relative humidity, and operating and shutdown conditions. However, excessive membrane hydration results in flooding, excessive swelling of the membranes and the formation of differential pressure gradients across the fuel cell stack.
Because the balance of water in a fuel cell is important to operation of the fuel cell, water management has a major impact on the performance and durability of fuel cells. Fuel cell degradation with mass transport losses due to poor water management remains a concern for automotive applications. Long-term exposure of the membrane to water can also cause irreversible material degradation. Water management strategies such as the establishment of pressure and temperature gradients and counter flow operation have been implemented and have been found to reduce mass transport to some degree, especially at high current densities. However, optimum water management is still needed for optimum performance and durability of a fuel cell stack.
It is known that various surface features, such as faceted periodic surface structures in the form of pyramidal arrays, can be made by ion bombardment-induced sputtering on the surfaces of metals. Furthermore, an increase in surface area at the nanometer and micrometer length scales is the key to making super hydrophobic surfaces. Accordingly, the present invention proposes a method of enhancing fuel cell water management by surface modification of fuel cell components through ion bombardment of the surfaces. This creates super-hydrophobic surfaces which repel water, reducing retention of water on the surfaces and promoting mass transport of oxygen and water in the fuel cell.